User equipment and signal transmission method

ABSTRACT

There is provided user equipment that selects a resource for transmitting a signal based on a sensing result. The user equipment includes a detection unit that detects, by performing sensing in a time window for sensing, one or more resources capable of transmitting a signal in a time window for resource selection after the time window for sensing; a selection unit that selects a resource for transmitting a signal from the one or more detected resources; and a transmission unit that transmits the signal using the selected resource for transmitting the signal.

TECHNICAL FIELD

The present invention relates to user equipment and a signaltransmission method.

BACKGROUND ART

In Long Term Evolution (LTE) and successor systems (for example, alsoreferred to as LTE Advanced (LTE-A), 4G, Future Radio Access (FRA), 5G,and the like) of LTE, Device to Device (D2D) technology has been studiedin which units of user equipment directly communicate with each otherwithout going through a radio base station (for example, Non-PatentDocument 1).

D2D reduces the traffic between the user equipment and the base station,or enables communication between units of user equipment even in a casewhere communication with the base station is not possible in the eventof a disaster or the like.

D2D is classified roughly according to D2D discovery for finding othercommunicable units of user equipment and D2D communication (alsoreferred to as D2D direct communication, D2D communication,inter-terminal direct communication, and the like) for performing directcommunication between units of user equipment. Hereinafter, when D2Dcommunication, D2D discovery, and the like are not particularlydistinguished from each other, these are simply referred to as D2D. Inaddition, a signal transmitted and received by D2D is referred to as aD2D signal.

In addition, in 3rd Generation Partnership Project (3GPP), it has beenstudied to achieve V2X by extending the D2D function. Here, the V2X is apart of Intelligent Transport Systems (ITS). As shown in FIG. 1, the V2Xis a generic term for Vehicle to Vehicle (V2V) that means a mode ofcommunication performed between vehicles, Vehicle to Infrastructure(V2I) that means a mode of communication performed between a vehicle anda Road-Side Unit (RSU) installed at the side of the road, Vehicle toNomadic device (V2N) that means a mode of communication performedbetween a vehicle and a mobile terminal of the driver, and Vehicle toPedestrian (V2P) that means a mode of communication performed between avehicle and a mobile terminal of a pedestrian.

CITATION LIST Non-Patent Document

Non-Patent Document 1: “Key drivers for LTE success: ServicesEvolution”, September, 2011, 3GPP, Internet URL:http://www.3gpp.org/ftp/Information/presentations/presentations_2011/2011_09_LTE_Asia/2011_LTE-Asia_3GPP_Service_evolution.pdf

Non-Patent Document 2: 3GPP TS36.300 V13.2.0 (2015-12)

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

The technology of V2X is based on the technology of D2D specified inLTE. In the technology of D2D, a method in which user equipment selectsresources to transmit the D2D signal is classified roughly according toa method of dynamically allocating resources from a base station and amethod in which the user equipment autonomously selects resources. InV2X, especially, in V2V, since units of user equipment (for example,vehicles) are present at high density and move at high speed, the methodof dynamically allocating resources is not efficient. Accordingly, it isassumed that a method is to be used in which units of user equipmentautonomously select resources.

In addition, it is assumed that, in V2V, when the user equipmentautonomously selects resources, the selected resources aresemi-persistently used instead of selecting resources each time a packetis transmitted. Then, for example, when a problem (for example, aconflict) occurs in resources to be used, resources are reselected.

When a plurality of units of user equipment autonomously select(reselection is included) transmission resources, if each user equipmentfreely selects resources, a resource conflict occurs. Accordingly, theuser equipment on the reception side cannot appropriately receive thesignal.

Therefore, a sensing-based resource selection method for selectingresources, which are not used (occupied), by performing resource sensinghas been proposed. A specific example is shown with reference to FIG. 2.In the example shown in FIG. 2, it is assumed that a time window inwhich user equipment performs sensing (referred to as a “sensingwindow”) is set in advance and the size (period) of the sensing windowis set to be the same as a period at which the user equipment transmitsa packet semi-persistently. In the example shown in FIG. 2, the userequipment detects resources (A1 to D1), which are not occupied, byperforming sensing in a sensing window 1. Since it can be determinedthat the detected resources are not occupied in the next sensing window2, the user equipment considers resources (A2 to D2) corresponding tothe resources (A1 to D1) that are not occupied, in the next sensingwindow 2, to be resources capable of transmitting a D2D signal, andselects a resource (for example, A2) from the resources (A2 to D2) tostart transmission of the D2D signal.

However, in the resource selection method described above, since theuser equipment selects one of resources not occupied in the sensingwindow, there is a problem that a delay may occur particularly whentrying new communication depending on the resource to be selected. Forexample, in FIG. 2, in a case where the user equipment startstransmission of the D2D signal with the resource D2, there is a delayuntil the transmission of the D2D signal is started compared with a casewhere the transmission of the D2D signal is started with the resourceA2. On the other hand, it is also considered that user equipment UE cansuppress the delay by selecting the resource A2 capable of transmittingthe D2D signal at an earlier timing. However, if such an operation isallowed, in a case where a plurality of units of user equipment try toperform communication newly, there is a possibility that all of theunits of user equipment select the resource A2. As a result, signalcollision occurs between the units of user equipment UE.

Considering that V2X is a type of D2D, the above problem is not limitedto V2X, but is a problem that can occur in general in D2D.

The disclosed technique has been made in view of the above, and theobject is to provide a technique enabling appropriate communicationwhile reducing a delay in a method of selecting a resource fortransmitting a signal based on a sensing result.

Means for Solving Problem

User equipment of the disclosed technique is user equipment that selectsa resource for transmitting a signal based on a sensing result. The userequipment includes a detection unit that detects, by performing sensingin a time window for sensing, one or more resources capable oftransmitting a signal in a time window for resource selection after thetime window for sensing; a selection unit that selects a resource fortransmitting a signal from the one or more detected resources; and atransmission unit that transmits the signal using the selected resourcefor transmitting the signal.

Effect of the Invention

According to the disclosed technique, there is provided a techniqueenabling appropriate communication while reducing a delay in the methodof selecting a resource for transmitting a signal based on a sensingresult.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating V2X;

FIG. 2 is a diagram illustrating a problem;

FIG. 3A is a diagram illustrating D2D;

FIG. 3B is a diagram illustrating D2D;

FIG. 4 is a diagram illustrating MAC PDU used in D2D communication;

FIG. 5 is a diagram illustrating a format of SL-SCH subheader;

FIG. 6 is a diagram illustrating an example of the channel structureused in D2D;

FIG. 7A is a diagram illustrating the structure example of PSDCH;

FIG. 7B is a diagram illustrating the structure example of PSDCH;

FIG. 8A is a diagram illustrating the structure example of PSCCH andPSSCH;

FIG. 8B is a diagram illustrating the structure example of PSCCH andPSSCH;

FIG. 9A is a diagram illustrating a resource pool configuration;

FIG. 9B is a diagram illustrating a resource pool configuration;

FIG. 10 is a diagram illustrating an example of the configuration of aradio communication system according to an embodiment;

FIG. 11 is a diagram illustrating an example of a transmission operationperformed by user equipment;

FIG. 12 is a diagram illustrating a configuration method (configurationmethod 1) of the start timing and the end timing of each window;

FIG. 13 is a diagram illustrating a case where an offset is set in theconfiguration method (configuration method 1);

FIG. 14 is a diagram illustrating a case where resources to be selectedoverlap each other;

FIG. 15 is a diagram illustrating a configuration method (configurationmethod 2) of the start timing and the end timing of each window;

FIG. 16 is a diagram illustrating a case where an offset is set in theconfiguration method (configuration method 2);

FIG. 17 is a diagram illustrating a resource selection operation in acase where the priority is high;

FIG. 18 is a diagram illustrating a resource reservation operation whenthe priority is high;

FIG. 19 is a diagram illustrating an example of the functionalconfiguration of user equipment according to an embodiment;

FIG. 20 is a diagram illustrating an example of the functionalconfiguration of a base station according to an embodiment;

FIG. 21 is a diagram illustrating an example of the hardwareconfiguration of user equipment according to an embodiment; and

FIG. 22 is a diagram illustrating an example of the hardwareconfiguration of a base station according to an embodiment.

MODE(S) FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the invention will be described withreference to the diagrams. In addition, the embodiment described belowis merely an example, and embodiments to which the invention is appliedare not limited to the following embodiment. For example, a radiocommunication system according to the present embodiment is assumed tobe a system using a method based on the LTE. However, the invention isnot limited to the LTE, but can be applied to other methods. Inaddition, in this specification and the appended claims, “LTE” is usedin a broad sense including not only the communication methodcorresponding to the release 8 or 9 of 3GPP but also the fifthgeneration communication methods corresponding to the release 10, 11,12, and 13 or the release 14 and subsequent ones of 3GPP.

In addition, although the present embodiment is mainly for V2X, thetechnique according to the present embodiment is not limited to V2X butcan be applied to D2D in general. In addition, “D2D” includes V2X as itsmeaning.

In addition, “D2D” is used in a broad sense including not only a processfor transmitting and receiving the D2D signal between the units of userequipment UE but also a process, in which the base station receives(monitors) the D2D signal, and a process, in which the user equipment UEtransmits an uplink signal to a base station eNB in the case of RRC idleor in a case where a connection with the base station eNB is notestablished.

<Overview of D2D>

An overview of D2D specified in LTE will be described. In addition, alsoin V2X, it is possible to use the technology of D2D described herein,and the UE according to the embodiment of the invention can transmit andreceive the D2D signal using the technology.

As already described, D2D is roughly divided into “D2D discovery” and“D2D communication”. For “D2D discovery”, as shown in FIG. 3A, for eachDiscovery period, a resource pool for a Discovery message is secured,and the user equipment UE transmits a Discovery message (discoverysignal) in the resource pool. More specifically, there are Type 1 andType 2b. In Type 1, the user equipment UE autonomously selects atransmission resource from the resource pool. In Type 2b, quasi-staticresources can be allocated by upper layer signaling (for example, RRCsignal).

Also for “D2D communication”, as shown in FIG. 3B, a resource pool forSCI/data transmission is periodically secured. The user equipment UE onthe transmission side notifies the reception side of resources for datatransmission (PSSCH resource pool) or the like by the SCI with aresource selected from the Control resource pool (PSCCH resource pool),and transmits data with the resources for data transmission. For moredetails on “D2D communication”, there are Mode 1 and Mode 2. In Mode 1,resources are dynamically allocated by (E) PDCCH transmitted to the userequipment UE from the base station eNB. In Mode 2, the user equipment UEautonomously selects a transmission resource from the resource pool. Aresource pool is notified by SIB, or a resource pool defined in advanceis used.

In LTE, a channel used in “D2D discovery” is referred to as a PhysicalSidelink Discovery Channel (PSDCH), a channel for transmitting controlinformation, such as SCI, in “D2D communication” is referred to as aPhysical Sidelink Control Channel (PSCCH), and a channel fortransmitting data is referred to as a Physical Sidelink Shared Channel(PSSCH) (Non-Patent Document 2).

As shown in FIG. 4, a Medium Access Control (MAC) Protocol Data Unit(PDU) used in D2D communication is configured to include at least MACheader, MAC Control element, MAC Service Data Unit (SDU), and Padding.The MAC PDU may also include other pieces of information. The MAC headerincludes one Sidelink Shared Channel (SL-SCH) subheader and one or moreMAC PDU subheaders.

As shown in FIG. 5, the SL-SCH subheader includes MAC PDU formatversion, transmission source information (SRC), transmission destinationinformation (DST), Reserved bit (R), and the like. V is allocated to thehead of the SL-SCH subheader, and indicates a MAC PDU format versionused by the user equipment UE. Information regarding the transmissionsource is set in the transmission source information. An identifier forProSe UE ID may be set in the transmission source information.Information regarding the transmission destination is set in thetransmission destination information. Information regarding ProSeLayer-2 Group ID of the transmission destination may be set in thetransmission destination information.

FIG. 6 shows an example of the channel structure of D2D. As shown inFIG. 6, a resource pool of PSCCH and a resource pool of PSSCH that areused in “D2D communication” are allocated. In addition, a resource poolof PSDCH used in “D2D discovery” is allocated at a period longer thanthe period of the channel of “D2D communication”.

In addition, a Primary Sidelink Synchronization signal (PSSS) and aSecondary Sidelink Synchronization signal (SSSS) are used assynchronizing signals for D2D. In addition, a Physical SidelinkBroadcast Channel (PSBCH) for transmitting broadcast information of asystem band of D2D, a frame number, resource configuration information,and the like is used, for example, for operation outside coverage.

FIG. 7A shows an example of a resource pool of PSDCH used in “D2Ddiscovery”. Since the resource pool is set by the bitmap of thesubframe, the resource pool becomes a resource pool of an image shown inFIG. 7A. This is the same for the resource pools of other channels. Inaddition, PSDCH is repeatedly transmitted (repetition) while performingfrequency hopping. The number of repetitions can be set to, for example,0 to 4. In addition, as shown in FIG. 7B, PSDCH has a PUSCH basedstructure, and has a structure in which demodulation reference signal(DM-RS) is inserted.

FIG. 8A shows examples of resource pools of PSCCH and PSSCH used in “D2Dcommunication”. As shown in FIG. 8A, PSCCH is repeatedly transmitted(repetition) twice including the first time while performing frequencyhopping. PSCCH is repeatedly transmitted (repetition) four timesincluding the first time while performing frequency hopping. Inaddition, as shown in FIG. 8B, PSCCH and PSSCH have a PUSCH basedstructure, and have a structure in which DM-RS is inserted.

FIGS. 9A-9B show an example of the resource pool configuration in PSCCH,PSDCH, and PSSCH (Mode 2). As shown in FIG. 9A, in a time direction, theresource pool is expressed as a subframe bitmap. In addition, the bitmapis repeated by the number of times of num. reprtition. In addition,offset indicating the start position in each period is designated.

In a frequency direction, contiguous allocation and non-contiguousallocation are possible. FIG. 9B shows an example of non-contiguous. Asshown in FIG. 9B, start PRB, End PRB, and the number of PRBs (numPRB)are designated.

<System Configuration>

FIG. 10 is a diagram showing an example of the configuration of theradio communication system according to the embodiment. As shown in FIG.10, the radio communication system according to the present embodimenthas the base station eNB, user equipment UE1, and user equipment UE2. InFIG. 10, it is intended that the user equipment UE1 is a transmissionside and the user equipment UE2 is a reception side. However, each ofthe user equipment UE1 and the user equipment UE2 has both atransmission function and a reception function. Hereinafter, in a casewhere the user equipment UE1 and the user equipment UE2 are notparticularly distinguished from each other, the user equipment is simplydescribed as the “user equipment UE”.

Each of the user equipment UE1 and the user equipment UE2 shown in FIG.10 has a function of cellular communication as the user equipment UE inLTE and a D2D function including signal transmission and reception inthe above-described channels. In addition, each of the user equipmentUE1 and the user equipment UE2 has a function of executing the operationdescribed in the present embodiment. In addition, for the function ofcellular communication and the function of the existing D2D, each of theuser equipment UE1 and the user equipment UE2 may have only some of thefunctions (range in which the operation described in the presentembodiment can be executed), or may have all the functions.

In addition, although each user equipment UE may be any device havingthe function of D2D, each user equipment UE is, for example, a vehicle,a terminal held by a pedestrian, or an RSU (UE type RSU having a UEfunction).

In addition, for the base station eNB, each user equipment UE has afunction of cellular communication as the base station eNB in LTE andfunctions (a resource allocation function, a configuration informationnotification function, and the like) for enabling the communication ofthe user equipment UE in the present embodiment. In addition, the basestation eNB includes an RSU (eNB type RSU having an eNB function).

Basically, in the present embodiment, the user equipment UE selectsresources, which are not occupied, by performing sensing in a sensingwindow, and periodically transmits a D2D signal semi-persistently usingthe selected resources. “Sensing” is performed, for example, using amethod of measuring received power (may be referred to as receivedenergy or received intensity), or by receiving the SCI transmitted fromother units of user equipment UE, decoding the SCI, and detecting theresource positions of the allocated SCI and data, or by combining these.“Resource” includes a time resource (for example, a subframe) or a timeand frequency resource (for example, a subchannel) unless otherwisenoted. “D2D signal” may be SCI, or may be data, or may be a set of SCIand data. In addition, the D2D signal may be a discovery signal.

<Regarding Resource Selection and Transmission Operation>

(Regarding a Selection Window)

Subsequently, a resource selection method when the user equipment UEaccording to the present embodiment intends to start transmission of theD2D signal and an operation of transmitting the D2D signal will bedescribed. In the sensing-based resource selection method described withreference to FIG. 2, the user equipment UE detects resources, which arenot occupied, by performing sensing in a sensing window, and selects aresource from resources capable of transmitting a signal in the nextsensing window to start transmission of the D2D signal.

On the other hand, in the present embodiment, a time window(hereinafter, referred to as a “selection window”) indicating a rangefor selecting a resource to transmit the D2D signal is provided in atime window corresponding to the next sensing window, and the userequipment UE selects one of the resources in the selection window tostart transmission of the D2D signal.

FIG. 11 is a diagram illustrating an example of a transmission operationperformed by the user equipment. For example, it is assumed that theuser equipment UE detects resources (A1 to F1), which are not occupied,by performing sensing in a sensing window. In this case, in the resourceselection method described above, the user equipment UE startstransmission of the D2D signal using any resource among resources (A2 toF2) capable of transmitting the D2D signal. On the other hand, in thepresent embodiment, the user equipment UE starts transmission of the D2Dsignal using any resource among the resources (A2 to C2) correspondingto the selection window. Therefore, since the user equipment UE selectsa resource in the limited selection window, it is possible to shortenthe delay required from the time when it is determined to transmit theD2D signal until the actual transmission of the D2D signal is started.In addition, by providing the selection window, it is possible toshorten the delay more effectively particularly in a case where a periodof transmitting the D2D signal semi-persistently is long (that is, in acase where the size of the sensing window is long).

The selection window is set after the sensing window. The size of theselection window needs to be set to at most the size of the sensingwindow or less. In addition, considering the effect of delay reduction,it is preferable that the size of the selection window is shorter thanthe size of the sensing window. In addition, the selection window doesnot necessarily need to be set subsequent to the sensing window. Forexample, it is also possible to set the start timing of the selectionwindow after a predetermined offset (after several subframes or thelike) from the end timing of the sensing window.

(Regarding a Reservation Window)

In the present embodiment, the user equipment UE selects a resource inthe selection window to start transmission of the D2D signal, but it isalso assumed that it is desired to start transmission of the D2D signaloutside the range of the selection window. For example, in FIG. 11, itis also assumed that it is desired to start transmission of the D2Dsignal using the resource E2. In order to respond to such a case, in thepresent embodiment, a time window (hereinafter, referred to as a“reservation window”) indicating a range in which a resource can bereserved may be provided in a time window corresponding to the nextsensing window, so that the user equipment UE can reserve a resourcewithin the reservation window.

For example, in a case where it is necessary to start transmission ofthe D2D signal with the resource E2, the user equipment UE selects oneof the resources A2 to C2 in the selection window, and transmits a D2Dsignal including reservation information, which indicates that theresource E2 is reserved, with the selected resource. Therefore, otherunits of user equipment UE that have received the reservationinformation can detect that the resource E2 is reserved. In addition,the reservation information may include configuration informationindicating a period of transmitting the D2D signal semi-persistently.

In order to avoid resource conflicts, the size of the reservation windowneeds to be set to at most the size of the sensing window or less. Inaddition, the reservation window and the selection windows may overlapeach other, or may be set subsequent to the selection window. Thereservation window can be set to the size of the sensing window or lessby using a predetermined window or a window set from the base stationeNB.

While it is effective to reduce the delay at the time of resourceconflict by enabling resource reservation to reduce the probability ofresource conflict, excessive resource reservation of the user equipmentUE may restrict selectable resources of the other units of userequipment UE. The reservation window is also effective for suppressingsuch excessive resource reservation. For example, the base station eNBmay set the reservation window using upper layer signaling (RRC messageor the like) or broadcast information (SIB), or the window size that canbe reserved by the user equipment UE may be limited in advance. For suchpurpose, the base station eNB may limit the number of resources that canbe reserved, the number of reservation processes, the number of times oftransmission of the D2D signals, or/and the time occupancy of resourcesfor transmitting the D2D signal instead of the reservation window or inaddition to the reservation window. For example, in a case where thenumber of reservation processes is limited to 1, the user equipment UEreserves only a resource that can be scheduled with one MAC PDU or oneSCI transmission. In addition, the user equipment UE may transmit asignaling notifying that the reservation resource is to be released.Therefore, an effect of releasing resources, which are not necessary forthe user equipment UE, is also expected.

In the case of charging for the transmission of the D2D signal, there isa method of causing the user equipment UE to report the number oftransmission bits to the network for charging. In this case, datatransmission may always be performed unless the release notice of theresource reserved by the user equipment UE is not given, or the userequipment UE may be made to perform an operation of adding the number oftransmission bits to the bill on the assumption that data has alwaysbeen transmitted unless the release notice of the reserved resource isnot given. In the latter case, it is necessary to determine ModulationCoding Scheme (MCS) for converting the number of transmission bits. Thismay be calculated based on the most recently selected MCS. For example,this may be calculated using an MCS scheduled to be used fortransmission of data corresponding to SCI including reservationinformation or the number of bits of the data. In addition, the abovemay be realized using a predetermined MCS or an MCS set from the basestation eNB instead of the most recently selected MCS.

(Regarding a Sensing Window)

In the present embodiment, the size of the sensing window may be set tobe the same as a period (Semi-Persistent scheduling (SPS) period), atwhich the user equipment UE transmits a packet semi-persistently, or atime interval, at which resource reservation is possible (period atwhich resource reservation is possible), or may be set to M times (M isan integer of 1 or more) the period. For example, in a case where theSPS period or the time interval at which resource reservation ispossible is 100 ms, the sensing window may be set to 100 ms, 200 ms, 300ms, or the like. In addition, in a case where the SPS period or the timeinterval at which resource reservation is possible differs between theunits of user equipment UE, it is preferable to set the size of thesensing window to M times (M is an integer of 1 or more) the longestperiod.

(Regarding a Resource Selection Method in a Selection Window)

As shown in FIG. 11, in a case where there are a plurality of resources(selectable resources) capable of transmitting the D2D signal in theselection window, the user equipment UE may randomly select a resourcefrom the plurality of resources. In a case where there are a pluralityof units of user equipment UE, resources selected among the units ofuser equipment UE are randomized.

In addition, as another method, the user equipment UE may select aresource from a plurality of resources based on predeterminedconditions. The predetermined conditions may be any conditions. Forexample, the predetermined conditions may be the quality (for example, achannel state of peripheral resources) of a channel, or may be whetheror not it is possible to transmit the D2D signal with the resource (forexample, it is scheduled to transmit a UL signal to the base station eNBor a gap where the D2D signal can be transmitted from the base stationeNB is set), or may be whether or not it is necessary to monitor otherD2D signals on the resource, or may be how much delay is allowed. Forexample, in a case where the user equipment UE is connected to a partother than the Sidelink carrier (carrier capable of transmitting the D2Dsignal), in a case where a gap where the D2D signal can be transmittedand received is set, the user equipment UE may select a resource only insubframes within the gap where the D2D signal can be transmitted, or mayperform sensing only in subframes within the gap where the D2D signalcan be received. By applying these operations in a case where thetransmission and reception capability of the user equipment UE isinsufficient, it is possible to perform efficient switching betweencarriers of a transceiver.

In addition, the user equipment UE may determine autonomously or basedon an instruction from the base station eNB whether to randomly select aresource from a plurality of resources or to select a resource from aplurality of resources based on predetermined conditions.

(Supplementary Matters Regarding Resource Selection and TransmissionOperation)

In the present embodiment, the user equipment UE does not need toperform sensing again before actually transmitting the D2D signal afterselecting the resource to transmit the D2D signal in the selectionwindow.

In addition, in the case of transmitting the D2D signalsemi-persistently, the user equipment UE needs only to perform sensingwhen starting transmission of the D2D signal first, and does not need toperform sensing again before transmitting the D2D signal periodicallyfrom the second time. In addition, the user equipment UE may performsensing in the background (that is, may perform sensing at a timing(subframe) at which no D2D signal is transmitted), and reselect aresource in a case where the possibility of signal collision withanother user equipment UE is detected.

<Regarding a Configuration Method of Start Timing and End Timing of EachWindow>

Subsequently, a configuration method and a recognition method of thestart timing and the end timing of the sensing window, the selectionwindow, and the reservation window will be described.

(Configuration Method 1)

In configuration method 1, the start timing and the end timing of thesensing window, the selection window, and the reservation window aredynamically determined based on a timing at which the user equipment UEselects a resource for transmitting the D2D signal. The timing at whichthe user equipment UE selects a resource for transmitting the D2D signalis, for example, a timing at which a transmission packet is generated byan upper layer (for example, a V2X application) and notification of thepresence of a transmission packet is sent to a layer (for example, anMAC layer or a physical layer) for selecting a resource.

FIG. 12 is a diagram illustrating the configuration method(configuration method 1) of the start timing and the end timing of eachwindow. In FIG. 12, it is assumed that the size of the sensing window is(X), the size of the selection window is (Y), and the size of thereservation window is (Z).

Assuming that the timing at which the user equipment UE selects aresource for transmitting the D2D signal is a subframe (n), the starttiming and the end timing of the sensing window are a subframe (n−X−1)and a subframe (n−1), respectively. In addition, the start timing andthe end timing of the selection window are the subframe (n) and asubframe (n+Y−1), respectively. In addition, the start timing and theend timing of the reservation window are the subframe (n) and a subframe(n+Z−1), respectively. That is, in the configuration method 1, the starttiming and the end timing of the sensing window, the selection window,and the reservation window slide according to the passage of time. Inaddition, since the sensing window has already been completed at thetiming at which the user equipment UE selects a resource fortransmitting the D2D signal, the user equipment UE needs to performsensing regardless of the presence or absence of a packet (D2D signal),which is to be transmitted, in order to check resources that can betransmitted.

According to the configuration method 1, since the start timing of theselection window matches a timing at which the user equipment UE startsan operation of selecting a resource for transmitting the D2D signal,the user equipment UE can start transmission of the D2D signal with aslittle delay as possible.

[Supplementary Matters Regarding the Configuration Method 1]

FIG. 13 shows an example of a case of setting an offset (O) between theend timing of the sensing window and the start timing of the selectionwindow in the configuration method 1. By providing the offset, the D2Dsignal can be actually transmitted after the offset time has passed fromthe generation of the D2D signal to be transmitted. Therefore, it ispossible to reduce the processing load on the user equipment UE.

In the configuration method 1, the size of the selection window may belimited to one subframe. This allows the user equipment UE to starttransmitting the D2D signal with a minimum delay although thepossibility of signal collision between the units of user equipment UEincreases.

In the configuration method 1, a case is assumed in which, in the caseof trying to transmit the D2D signal with a selected resource, anotheruser equipment UE selects the same resource. Explanation will be givenspecifically with reference to FIG. 14. For example, it is assumed thatthe user equipment UE1 selects a resource A of a subframe (n+3) byperforming an operation of selecting a resource for transmitting the D2Dsignal at the timing of the subframe (n). In this case, it is furtherassumed that the user equipment UE2 selects the resource A by performingan operation of selecting a resource for transmitting the D2D signal atthe timing of the subframe (n+3). In this case, since both the userequipment UE1 and the user equipment UE2 transmit the D2D signal withthe resource A, signal collision occurs. Therefore, in order to avoidsuch a situation, the user equipment UE may transmit a D2D signal (forexample, SCI), which includes reservation information indicating thatthe selected resource is reserved, at the timing of selecting a resourcefor transmitting the D2D signal. Specifically, the user equipment UE1may transmit the D2D signal including reservation information indicatingthat the resource A is reserved at the timing of the subframe (n) inFIG. 14. Therefore, since the user equipment UE2 can receive the D2Dsignal and recognize that the resource A is reserved, it is possible toavoid the selection of the resource A.

In the present embodiment, in a case where D2D communication isperformed such that the same SCI and data are repeatedly transmittedwithin the SC period, configuration method 2 to be described later maybe applied, or a part of the start timing or the end timing of eachwindow may be adjusted to the timing of the boundary of the SC period inthe configuration method 1.

(Configuration Method 2)

In the configuration method 2, the start timing and the end timing ofthe sensing window, the selection window, and the reservation window areadjusted to the timing of the boundary of a periodic period set inadvance. The periodic period set in advance may be an “SC period”, ormay be other periodic periods without being limited thereto.Hereinafter, a case where the periodic period is the “SC period” will bedescribed as an example.

FIG. 15 is a diagram illustrating the configuration method(configuration method 2) of the start timing and the end timing of eachwindow. In FIG. 15, it is assumed that the size of the sensing window is(X), the size of the selection window is (Y), and the size of thereservation window is (Z).

In the configuration method 2, assuming that the timing at which theuser equipment UE selects a resource for transmitting the D2D signal isthe subframe (n), the start timing of the selection window correspondsto the boundary between the SC period including the subframe (n) and thenext SC period. Accordingly, depending on the timing of the subframe(n), the user equipment UE needs to wait for about one SC period at themaximum before starting transmission of the D2D signal. On the otherhand, in a case where D2D communication is performed such that the sameSCI and data are repeatedly transmitted within the SC period, forexample, as in the D2D technology (technology described in the above<Overview of D2D>) of 3GPPRel-12, the start timing and the end timing ofeach window match the boundary of the SC period in the configurationmethod 2. Therefore, since the user equipment UE can sense all the D2Dsignals that are repeatedly transmitted by the other units of userequipment UE, it is possible to more appropriately detect the occupancystatus of resources.

FIG. 16 shows an example of a case of setting the offset (O) between theend timing of the sensing window and the start timing of the selectionwindow in the configuration method 2. By providing the offset, even if aD2D signal to be transmitted is generated near the end timing of thesensing window, the D2D signal can be transmitted after the passage ofthe offset time. Therefore, it is possible to reduce the processing loadon the user equipment UE. In addition, in a case where the period oftransmitting the D2D signal semi-persistently almost matches theboundary of the SC period, even if the timing at which a packet to betransmitted arrives at the lower layer is delayed to pass the SC period,it is possible to transmit the D2D signal without waiting for the nextSC period. As a result, it is possible to minimize the delay.

<Method of Setting Start Timing and End Timing of Each Window in UserEquipment>

In the present embodiment, the start timing and the end timing of eachwindow may be set (notified) in the user equipment using the followingmethods.

In addition, in the case of setting the start timing and the end timingof each window in the user equipment UE, for example, theabove-described X, Y, Z, and O values may be set in the user equipmentUE, or the SFN and the subframe position corresponding to the starttiming and the end timing of each window may be set in the userequipment UE. Without being limited to these, the start timing and theend timing of each window may be set in the user equipment UE using anymethod.

As a first method, it is also possible to notify (broadcast) each userequipment UE of the start timing and the end timing of each window usingthe broadcast information (SIB) from the base station eNB. In addition,the start timing and the end timing of each window may be setindividually in the user equipment UE using the RRC signal from the basestation eNB, or may be pre-configured individually in the user equipmentUE through a Subscriber Identity Module (SIM) or a core network.

In the case of setting the start timing and the end timing of eachwindow individually in the user equipment UE, the base station eNB mayset different start timing and end timing in each user equipment UE. Inaddition, the base station eNB may change the start timing and the endtiming, which are set in each user equipment UE, according to apredetermined priority. The predetermined priority may be, for example,the priority of the user equipment UE itself, or may be the priority ofthe resource pool in which the user equipment UE transmits a V2X packetor the priority of a bearer (bearer used in D2D is assumed). This makesit possible, for example, to set the size of the selection window to besmaller than that of the normal user equipment UE for the user equipmentUE that needs to transmit a less delayed V2X packet.

In addition, in the case of setting the start timing and the end timingof each window individually in the user equipment UE, the user equipmentUE may ask the base station eNB about the start timing and the endtiming of each window each time the transmission of a V2X packet isperformed. In this case, the user equipment UE may ask the base stationeNB to notify the user equipment UE of the traffic type of the V2Xpacket, the congestion state of a cell (carrier), and the like.

In addition, the size of the offset (value of 0) may be set so as to bevariable according to the characteristics of the traffic(characteristics of the V2X packet) transmitted by the user equipmentUE. In addition, a value larger than a variation in timing at which apacket is periodically generated in an upper layer (V2X application orthe like) may be set. For example, a packet is generated at a period of100 ms. In practice, however, in a case where a deviation of about ±2 msoccurs, the size of the offset may be set to 3 ms or more (threesubframes or more).

As a second method, the user equipment UE may autonomously select anarbitrary candidate from candidates for the start timing and the endtiming of each window set in advance.

As a third method, the start timing and the end timing of each windowmay be fixedly associated with the SC period. For example, in theconfiguration method 2 described above, the values of X, Y, and Z may befixedly determined in advance by standard specifications or the like.

As a fourth method, the start timing and the end timing of each windowmay be fixedly determined. For example, in the configuration method 1described above, the values of X, Y, Z, and O may be fixedly determinedin advance by standard specifications or the like.

In addition, the base station eNB may allow the user equipment UE to setwhich method of the “configuration method 1” and the “configurationmethod 2” is to be used, in addition to the start timing and the endtiming of each window. In addition, the user equipment UE may supportboth the “configuration method 1” and the “configuration method 2”, ormay support only of the “configuration method 1” and the “configurationmethod 2”.

<Regarding Resource Selection/Resource Reservation According toPriority>

(Resource Selection Choice According to Priority)

In the “(resource selection method in a selection window)” describedabove, the user equipment UE randomly selects a resource from aplurality of resources or selects a resource from a plurality ofresources based on predetermined conditions. However, in V2X, it isassumed that the user equipment UE performs packet transmission with ahigh priority (for example, packet transmission for notification of theoccurrence of an accident). In addition, it is assumed that the userequipment UE with a high priority (for example, an emergency vehicle) isset apart from the normal user equipment UE (for example, a generalvehicle).

Therefore, in a case where the priority of a packet to be transmitted ishigh or in a case where the priority of the user equipment UE itself ishigh, the user equipment UE may select a resource with the least delayfrom a plurality of resources selectable in the selection window asshown in FIG. 17. In addition, as another method, in a case where theconfiguration method 1 described above is applied, the user equipment UEwith a high priority may set the size of the selection window to onesubframe.

(Resource Reservation According to Priority)

In a case where the priority of a packet to be transmitted is high or ina case where the priority of the user equipment UE itself is high, theuser equipment UE may reserve a resource beyond the range of thereservation window or within a wide reservation window set individuallyin the user equipment UE. For example, as shown in FIG. 18, areservation window corresponding to a case where the priority of apacket to be transmitted is high or a case where the priority of theuser equipment UE itself is high may be set, and the user equipment UEmay reserve a resource within the reservation window. Accordingly, forexample, even in a case where all the resources are reserved in thereservation window and accordingly it is not possible to transmit theD2D signal, the user equipment UE can transmit the D2D signal.

<Regarding an Operation in a Case where there is No Resource Capable ofTransmitting Signals in the Selection Window>

In a situation where many units of user equipment UE are transmittingD2D signals, a case is assumed in which there is no resource capable oftransmitting the D2D signal within the selection window. In addition, insuch a situation, even if a resource that can be transmitted isdetected, there is a high possibility that signal collision will occursince a plurality of units of user equipment UE select the resource.

Therefore, in the present embodiment, in a case where there is noresource that can be transmitted in the selection window, the userequipment UE may temporarily increase (for example, double) the size ofthe selection window with the size of the sensing window as an upperlimit. In this case, the user equipment UE causes the size of theselection window to return to the original size after selecting theresource. Accordingly, since a resource selected by each user equipmentUE is randomized, it is possible to reduce the possibility of signalcollision. The change of the sensing window size may be performedautonomously by the user equipment UE in a case where there is noselectable resource, or the user equipment UE may report that to thebase station eNB and the base station eNB may change the size of thesensing window using upper layer signaling (RRC message or the like) orbroadcast information (SIB). In the latter case, since it is possible toextend the sensing window including the neighboring user equipment UE, ahigh randomization effect is expected while the delay is large.

In addition, as another method, in a case where there is no resourcethat can be transmitted in the selection window, the user equipment UEmay select a resource again after a predetermined back off time haspassed. Although the predetermined back off time is arbitrary, thepredetermined back off time may be the same as the size of the sensingwindow, for example. In a case where the back off time is set to onesubframe, the probability of collision increases, but the delayaccording to resource reselection can be reduced. In addition, in a casewhere there is no resource that can be transmitted in the selectionwindow continuously, the predetermined back off time may be graduallyextended. For example, in a case where the predetermined back off timeis set to T time, the user equipment UE may operate such that the secondresource selection is performed after the passage of T time, the thirdresource selection is performed after the passage of T×2 (or T×4) time,and the fourth resource selection is performed after the passage of T×3(or T×6) time. Therefore, it is possible to avoid a situation in which aplurality of units of user equipment UE perform resource selectionfrequently and repeatedly. In addition, in order to randomize the backoff time between the units of user equipment UE, a back off time uniqueto the user equipment UE of T×N may be set in the user equipment UEusing a random value N within a certain range.

In addition, as another method, the user equipment UE may notify its ownupper layer (for example, a V2X application) or the base station eNBthat there is no resource that can be transmitted in the selectionwindow. Therefore, the upper layer of the user equipment UE candetermine that the radio resources are congested, and take measures suchas increasing the transmission period of the V2X packet. In addition, itis also possible to notify each user equipment UE that the radioresources are congested through the base station eNB.

In addition, in a broad sense, even a case of reselecting a resource bydetecting a resource conflict or the like can be regarded as a type ofthe case where there is no resource capable of transmitting the D2Dsignal in the selection window. Accordingly, an increase in the resourceconflict rate due to excessive resource reselection can be reduced byapplying the operation described in “<Regarding an operation in a casewhere there is no resource capable of transmitting signals in theselection window>”.

The extension of the selection window and the application of the backoff time described above are trade-offs between the resource conflictprobability and the delay due to resource reselection. Accordingly, thesize for extending the selection window and the back off time may be setsuch that different sizes and times are applied according to the userequipment UE and the priority of a packet. For example, parametersrelevant to each user equipment UE may be set from the base station eNB,or parameters may be defined in advance for each priority level, ornotification using broadcast information, pre-configuration, or the likemay be sent.

<Regarding Random Resource Selection>

The user equipment UE may use resource selection using sensing only atthe time of resource reselection, and may randomly select a resourcewithin the selection window without performing sensing in resourceselection at the time of first transmission. For example, the userequipment UE may start sensing in a case where a counter based on thenumber of times of transmission of the D2D signal or elapsed time aftertransmission start reaches a certain value, and may stop the sensingwhen the counter becomes equal to or less than the certain value byresetting of the counter due to resource selection or the like. In thiscase, it is not possible to use the sensing result when transmitting anew packet at an arbitrary timing. However, since it is not necessary toalways perform sensing in the background, it is possible to reduce thebattery consumption of the user equipment UE. Transmission resourcepools used in random resource selection and sensing-based resourceselection may be different. For example, a resource selection methodapplicable to each resource pool may be set (in advance) in the userequipment UE in the upper layer.

In addition, in a case where it is detected that the interference level(or RSSI) is equal to or greater than a predetermined threshold value asa result of sensing (Measurement), the user equipment UE may fall backto random resource selection from sensing-based resource selection.Since the number of candidates for resource selection increases, theinterference randomization effect is expected. The user equipment UE maydetermine whether or not to perform such an operation depending on thenumber of sensed resources and the number of sensed subframes, thenumber of candidates for selection resources, and/or terminalcapability. The threshold value of the interference level may be set (inadvance) in the user equipment UE in the upper layer. In addition, forexample, in a case where the number of selectable resources is equal toor less than a certain number (rate) as a result of sensing, the userequipment UE may fall back to random resource selection withoutadjusting the aforementioned predetermined threshold value or the like.In particular, since sensing is performed only for partial subframes,this is effective in a case where the number of resources to be selectedis small. In addition, in the case of using a method, such as selectinga resource from top X % resources with less interference, in sensing,the user equipment UE may change the rate according to the number ofsensed resources and the number of sensed subframes, the number ofcandidates for selection resources, and/or terminal capability. In acase where the absolute number of resource candidates is small, therandomization effect can be obtained by setting a larger value as X. Xmay be set according to the above-described conditions (the number ofsensed resources and the number of sensed subframes, the number ofcandidates for selection resources, and/or terminal capability), or maybe set (in advance) in the user equipment UE by upper layer signaling.In addition, the user equipment UE may perform random resource selectionin a case where the measurement result of top X % resources is equal toor greater than a predetermined threshold value.

The user equipment UE may change the size of the selection window thatcan be taken in the case of performing the sensing-based resourceselection and the case of performing the random resource selection. Forexample, in the case of performing the random resource selection, therandomization effect may be increased by specifying a larger selectionwindow size to be selected. The size of the selection window may be setfor each packet priority or resource pool.

The user equipment UE may relax the sensing procedure depending on theterminal capability or the resource pool setting. For example, althoughsensing can be configured to include a step based on decoding ormeasurement of control information and a step based on power detection(RSSI measurement or the like), the user equipment UE may execute onlythe step based on power detection between these steps. In this case,since the user equipment UE does not need blind detection of controlinformation, it is possible to reduce terminal cost and powerconsumption.

<Regarding Exclusion of Resource Selection Candidate>

In the embodiment described so far, in the case of transmitting the D2Dsignal semi-persistently, it is a prerequisite to allow the userequipment UE to perform sensing before starting transmission of the D2Dsignal first and to transmit the D2D signal with the selected resourcein the subsequent period. In addition, since the user equipment UEtransmits the D2D signal with periodic resources after the selectedresource, sensing is not performed (sensing is skipped) in resources fortransmitting the D2D signal from the second time. If the user equipmentUE operates in this manner, the same user equipment UE cannot continueto use the same resource. Therefore, in resources, for which sensing hasnot been performed (has been skipped) since the resources are resourcesfor transmitting the D2D signal, and the subsequent period, the userequipment UE may regard that the resources are occupied, and mayuniformly exclude the resources from the resource selection candidates.

However, if the resources are uniformly excluded from the resourceselection candidates, resource options that can be selected in theselection window are restricted. Therefore, as another method, insteadof uniformly excluding resources that have not been sensed and periodicresources thereafter from the resource selection candidate in theselection window, the user equipment UE may determine whether or not toexclude these resources from the resource selection candidates based onthe result of virtual measurement of the resources. Measuring resourcesvirtually refers to considering measurement results, which are set (inadvance), as measurement results in the corresponding resource. As aresult of virtual measurement of resources, for example, a measurementresult of resources of subframes different from resources to be measuredmay be used. In addition, in the same frequency domain as resources tobe measured, a measurement result of resources having a certain timerelationship with the resources may be used. In addition, the userequipment UE may prioritize the resource selection candidates based onthe result of virtual measurement of resources.

More specifically, for example, assuming that the subframe of a resourcefor which sensing has not been performed is n, a resources period (canalso be expressed as a resource reservation unit) is X, and k is apositive integer (may be limited to k=1, 2, 3, . . . , 10), the resourcefor which sensing has not been performed and periodic resourcesthereafter can be expressed as resources of subframes expressed asn+X×k. That is, instead of uniformly excluding the resources ofsubframes expressed as n+X×k from the resource selection candidates, theuser equipment UE may exclude the resources of subframes expressed asn+X×k from the resource selection candidates in a case where the virtualresource measurement result is equal to or greater than (or exceeds) apredetermined threshold value, and may determine the resources ofsubframes expressed as n+X×k as resource selection candidates in a casewhere the virtual resource measurement result is less than (or equal toor less than) the predetermined threshold value.

The virtual resource measurement result may be, for example,Sidelink-RSSI (S-RSSI), PSCCH-RSRP, or PSSCH-RSRP. More specifically,the virtual resource measurement result may be the power detectionresult of resources to be measured, the received power of DM-RStransmitted through PSCCH or PSSCH, or the like. The virtual resourcemeasurement result may be pre-configured in the user equipment UE, ormay be set in the user equipment UE using broadcast information (SIB) orRRC signaling. By setting “+ infinity” for the virtual resourcemeasurement result, it is possible to uniformly exclude the resourcessubstantially from the resource selection candidates. Conversely, bysetting “− infinity” for the virtual resource measurement result, it ispossible to set the resources substantially as resource selectioncandidates.

In addition, the predetermined threshold value may be a predefinedvalue, or may be pre-configured in the user equipment UE, or may be setin the user equipment UE using broadcast information (SIB) or RRCsignaling.

In addition, the virtual resource measurement result and thepredetermined threshold value can be set for each of priorityinformation of a packet transmitted by the user equipment UE, a resourcepool, and a carrier for transmitting the D2D signal. For example, for apacket with high priority, by setting a small value for the virtualresource measurement result, it is possible to increase a transmissionopportunity. In addition, the virtual resource measurement result may bemade to be variable according to the size of the resource selectionwindow.

Through the operation described above, the user equipment UE cansuppress unnecessary restrictions on the resource options that can beselected in the selection window. In addition, even in a case where thelength of the selection window is short, it is possible to secureresource options.

<Functional Configuration>

Functional configuration examples of the user equipment UE and the basestation eNB that perform the operations of the above-described pluralityof embodiments will be described.

(User Equipment)

FIG. 19 is a diagram showing an example of the functional configurationof user equipment according to an embodiment. As shown in FIG. 19, theuser equipment UE has a signal transmission unit 101, a signal receivingunit 102, a detection unit 103, and a selection unit 104. In addition,FIG. 19 shows only functional units particularly relevant to theembodiment of the invention in the user equipment UE, and there is alsoa function (not shown) for performing at least an operation conformingto LTE. In addition, the functional configuration shown in FIG. 19 isjust an example. As long as the operation according to the presentembodiment can be performed, any functional division and any name ofeach functional unit can be used. However, a part of the processing(some of the configuration methods, selection methods, or the like) ofthe user equipment UE described so far may be executable.

The signal transmission unit 101 includes a function of generatingvarious kinds of signals of the physical layer from signals of the upperlayer to be transmitted from the user equipment UE and wirelesslytransmitting the signals. In addition, the signal transmission unit 101has a D2D signal transmission function and a transmission function ofcellular communication. In addition, the signal transmission unit 101has a function of transmitting the D2D signal using a resource selectedby the selection unit 104.

In addition, the signal transmission unit 101 may transmit reservationinformation, which indicates that transmission of a signal is scheduledwith the “resource for reserving transmission of the D2D signal”selected by the selection unit 104, using the resource for transmittingthe D2D signal.

The signal receiving unit 102 includes a function of wirelesslyreceiving various kinds of signals from the other units of userequipment UE or the base station eNB and acquiring a signal of a higherlayer from the received signal of the physical layer. In addition, thesignal receiving unit 102 has a D2D signal receiving function and areception function of cellular communication.

The detection unit 103 has a function of detecting one or more resourcescapable of transmitting the D2D signal in the selection window after thesensing window by performing sensing in the sensing window. In addition,the detection unit 103 may detect one or more resources capable ofreserving transmission of the D2D signal in the reservation window afterthe sensing window by performing sensing in the sensing window. Inaddition, the detection unit 103 may virtually measure the receptionquality of periodic resources by performing sensing in the sensingwindow for periodic resources after a resource selected in the selectionwindow, and detect one or more resources capable of transmitting the D2Dsignal in the selection window based on the measured virtual receptionquality. In addition, the detection unit 103 may determine that aresource, for which the measured virtual reception quality is equal toor less than a predetermined threshold value, is a resource that cantransmit the D2D signal in the selection window. In addition, thedetection unit 103 may determine that a resource, for which the measuredvirtual reception quality is equal to or greater than a predeterminedthreshold value, is not a resource that can transmit the D2D signal inthe selection window.

The selection unit 104 has a function of selecting a resource fortransmitting the D2D signal from one or more resources detected by thedetection unit 103. In addition, in a case where a plurality ofresources are detected by the detection unit 103, the selection unit 104may determine autonomously or based on an instruction from the basestation eNB whether to randomly select a resource for transmitting theD2D signal from the plurality of resources or to select a resource basedon predetermined conditions. In addition, the selection unit 104 mayselect a resource for reserving transmission of the D2D signal from oneor more resources that can reserve transmission of the D2D signaldetected by the detection unit 103.

(Base Station)

FIG. 20 is a diagram showing an example of the functional configurationof a base station according to an embodiment. As shown in FIG. 20, thebase station eNB has a signal transmission unit 201, a signal receivingunit 202, and a notification unit 203. In addition, FIG. 20 shows onlyfunctional units particularly relevant to the embodiment of theinvention in the base station eNB, and there is also a function (notshown) for performing at least an operation conforming to LTE. Inaddition, the functional configuration shown in FIG. 20 is just anexample. As long as the operation according to the present embodimentcan be performed, any functional division and any name of eachfunctional unit can be used.

The signal transmission unit 201 includes a function of generatingvarious kinds of signals of the physical layer from signals of the upperlayer to be transmitted from the base station eNB and wirelesslytransmitting the signals. The signal receiving unit 202 includes afunction of wirelessly receiving various kinds of signals from the userequipment UE and acquiring a signal of a higher layer from the receivedsignal of the physical layer.

The notification unit 203 notifies the user equipment UE of variouskinds of information, which are used when the user equipment UE performsthe operation according to the present embodiment, using the broadcastinformation (SIB) or RRC signaling. In addition, the various kinds ofinformation are, for example, information indicating the configurationof a resource pool, information indicating the position of the SCperiod, information indicating the start timing and the end timing ofeach window (a sensing window, a selection window, and a reservationwindow), information indicating which method of “configuration method 1”and “configuration method 2” is to be used, and the like.

The entire functional configuration of each of the user equipment UE andthe base station eNB described above may be realized by a hardwarecircuit (for example, one or more IC chips), or a part of the functionalconfiguration of each of the user equipment UE and the base station eNBdescribed above may be formed by a hardware circuit and the other partsmay be realized by a CPU and a program.

(User Equipment)

FIG. 21 is a diagram showing an example of the hardware configuration ofuser equipment according to an embodiment. FIG. 21 shows a configurationsimilar to that of the implementation example as compared with FIG. 19.As shown in FIG. 21, the user equipment UE has an Radio Frequency (RF)module 301 for performing processing relevant to radio signals, a BaseBand (BB) processing module 302 for performing baseband signalprocessing, and a UE control module 303 for performing upper layerprocessing or the like.

The RF module 301 generates a radio signal to be transmitted from theantenna by performing Digital-to-Analog (D/A) conversion, modulation,frequency conversion, power amplification, and the like on the digitalbaseband signal received from the BB processing module 302. In addition,the RF module 301 generates a digital baseband signal by performingfrequency conversion, Analog to Digital (A/D) conversion, demodulation,and the like on the received radio signal, and transmits the digitalbaseband signal to the BB processing module 302. The RF module 301includes, for example, a part of the signal transmission unit 101 and apart of the signal receiving unit 102, all of which are shown in FIG.19.

The BB processing module 302 performs processing for converting the IPpacket and the digital baseband signal to each other. A Digital SignalProcessor (DSP) 312 is a processor that performs signal processing inthe BB processing module 302. A memory 322 is used as a work area of theDSP 312. The BB processing module 302 includes, for example, a part ofthe signal transmission unit 101, a part of the signal receiving unit102, the detection unit 103, and the selection unit 104, all of whichare shown in FIG. 19.

The UE control module 303 performs IP layer protocol processing, variouskinds of application processing, and the like. A processor 313 is aprocessor that performs the processing performed by the UE controlmodule 303. A memory 323 is used as a work area of the processor 313.

(Base Station)

FIG. 22 is a diagram showing an example of the hardware configuration ofa base station according to an embodiment. FIG. 22 shows a configurationsimilar to that of the implementation example as compared with FIG. 20.As shown in FIG. 20, the base station eNB has an RF module 401 forperforming processing relevant to radio signals, a BB processing module402 for performing baseband signal processing, a device control module403 for performing upper layer processing or the like, and acommunication IF 404 that is an interface for connection to a network.

The RF module 401 generates a radio signal to be transmitted from theantenna by performing D/A conversion, modulation, frequency conversion,power amplification, and the like on the digital baseband signalreceived from the BB processing module 402. In addition, the RF module401 generates a digital baseband signal by performing frequencyconversion, A/D conversion, demodulation, and the like on the receivedradio signal, and transmits the digital baseband signal to the BBprocessing module 302. The RF module 401 includes, for example, a partof the signal transmission unit 201 and a part of the signal receivingunit 202, all of which are shown in FIG. 20.

The BB processing module 402 performs processing for converting the IPpacket and the digital baseband signal to each other. A DSP 412 is aprocessor that performs signal processing in the BB processing module402. A memory 422 is used as a work area of the DSP 412. The BBprocessing module 402 includes, for example, a part of the signaltransmission unit 201 and a part of the signal receiving unit 202, allof which are shown in FIG. 20.

The device control module 403 performs IP layer protocol processing,Operation and Maintenance (OAM) processing, and the like. A processor413 is a processor that performs the processing performed by the devicecontrol module 403. A memory 423 is used as a work area of the processor413. An auxiliary storage device 433 is, for example, an HDD, and storesvarious kinds of configuration information and the like required for thebase station eNB itself to operate. The device control module 403includes, for example, the notification unit 203 shown in FIG. 20.

<Summary>

As described above, according to the embodiment, there is provided userequipment that selects a resource for transmitting a signal based on asensing result. The user equipment includes: a detection unit thatdetects one or more resources capable of transmitting a signal in a timewindow for resource selection after a time window for sensing byperforming sensing in the time window for sensing; a selection unit thatselects a resource for transmitting a signal from one or more detectedresources; and a transmission unit that transmits a signal using theselected resource for transmitting the signal. By the user equipment UE,there is provided a technique enabling appropriate communication whilereducing a delay in the method of selecting a resource for transmittinga signal based on the sensing result.

In addition, the time window for resource selection may be shorter thanthe time window for sensing. Therefore, since the user equipment UEselects a resource in the selection window shorter than the sensingwindow, it is possible to shorten the delay required from the time whenit is determined to transmit the D2D signal until the actualtransmission of the D2D signal is started.

In addition, in a case where a plurality of resources are detected bythe detection unit, the selection unit may determine autonomously orbased on an instruction from a base station whether to randomly select aresource for transmitting the signal from the plurality of resources orto select a resource for transmitting the signal based on predeterminedconditions. Therefore, in a case where a plurality of resources areselectable in the selection window, the user equipment UE can select aresource using various methods. In addition, in the case where of randomselection, it is possible to randomize the possibility of D2D signalcollision among a plurality of units of user equipment UE.

In addition, the start timing and the end timing of the time window forsensing and the start timing and the end timing of the time window forresource selection may be dynamically determined based on a timing atwhich the selection unit selects a resource for transmitting a signal,or may correspond to the timings of a boundary of a periodic period setin advance. In a case where the start timing and the end timing of thetime window for sensing and the start timing and the end timing of thetime window for resource selection are dynamically determined, the starttiming of the selection window matches a timing at which the userequipment UE starts an operation of selecting a resource fortransmitting the D2D signal. Accordingly, the user equipment UE canstart transmission of the D2D signal with as little delay as possible.In addition, in a case where the start timing and the end timing of eachwindow correspond to the timing of the boundary of a periodic period setin advance, the user equipment UE can sense all the D2D signals that arerepeatedly transmitted in a case where other units of user equipment UEtransmit the D2D signals repeatedly in the periodic period. Therefore,it is possible to more appropriately detect the occupancy status ofresources.

In addition, the detection unit may detect one or more resources capableof reserving transmission of a signal in a time window for resourcereservation after the time window for sensing by performing sensing inthe time window for sensing. The selection unit may select a resourcefor reserving transmission of a signal from the one or more detectedresources capable of reserving transmission of a signal. Thetransmission unit may transmit reservation information, which indicatesthat a signal is scheduled to be transmitted with a resource forreserving transmission of the signal, using a resource for transmittingthe signal. Therefore, since the user equipment UE can reserve aresource, it is possible to reduce a possibility that the D2D signaltransmitted by the other units of user equipment UE will interfere withthe D2D signal transmitted by the user equipment UE itself.

In addition, the detection unit may virtually measure a receptionquality of periodic resources by performing sensing in the time windowfor sensing for periodic resources after the selected resource fortransmitting the signal, and detect one or more resources capable oftransmitting a signal in the time window for resource selection based onthe measured virtual reception quality. Therefore, the user equipment UEcan suppress unnecessary restrictions on the resource options that canbe selected in the selection window.

In addition, according to an embodiment, there is provided a signaltransmission method executed by user equipment that selects a resourcefor transmitting a signal based on a sensing result. The signaltransmission method includes: a step of detecting one or more resourcescapable of transmitting a signal in a time window for resource selectionafter a time window for sensing by performing sensing in the time windowfor sensing; a step of selecting a resource for transmitting a signalfrom one or more detected resources; and a step of transmitting a signalusing the selected resource for transmitting a signal. By the signaltransmission method, there is provided a technique enabling appropriatecommunication while reducing a delay in the method of selecting aresource for transmitting a signal based on the sensing result.

<Supplement to Embodiments>

The SC period may be referred to as a Scheduling Assignment Period (SAperiod), or may be referred to as a PSCCH period.

As described above, the configuration of each device (user equipmentUE/base station eNB) described in the embodiment of the invention may bea configuration realized by executing a program by a CPU (processor) ina device including a CPU and a memory, or may be a configurationrealized by hardware, such as a hardware circuit having a processinglogic described in the present embodiment, or a program and hardware maybe mixed.

While the embodiment of the invention has been described above, thedisclosed invention is not limited to such an embodiment, and thoseskilled in the art will understand various modifications, alternatives,substitutions, and the like. For easy understanding of the invention,explanations were made using specific numerical examples. However,unless otherwise noted, these numerical values are just examples and anysuitable value may be used. The division of items in the abovedescription is not essential to the invention, and the matters describedin two or more items may be used in combination when necessary or thematter described in a certain item may be applied to the matterdescribed in another item (unless inconsistent with each other). Theboundary of functional units or processing units in a functional blockdiagram does not necessarily correspond to the boundary of physicalcomponents. The operations of a plurality of functional units may beperformed by physically one component, or the operation of onefunctional unit may be performed by physically plural components. Thesequences and flowcharts described in the embodiment may be changed aslong as there is no inconsistency. For convenience of processingexplanation, the user equipment UE/base station eNB has been describedusing a functional block diagram. However, such a device may beimplemented by hardware or software or a combination thereof. Each ofsoftware operated by the processor provided in the user equipment UEaccording to the embodiment of the invention and software operated bythe processor provided in the base station eNB according to theembodiment of the invention may be stored in any suitable storagemedium, such as a random access memory (RAM), a flash memory, a readonly memory (ROM), an EPROM, an EEPROM, a register, a hard disk (HDD), aremovable disk, a CD-ROM, a database, and a server.

The sensing window is an example of the time window for sensing. Theselection window is an example of the time window for resourceselection. The reservation window is an example of the time window forresource reservation.

Information transmission (notification, reporting) may be performed notonly by methods described in an aspect/embodiment of the presentspecification but also a method other than those described in anaspect/embodiment of the present specification. For example, theinformation transmission may be performed by physical layer signaling(e.g., DCI (Downlink Control Information), UCI (Uplink ControlInformation)), upper layer signaling (e.g., RRC signaling, MACsignaling, broadcast information (MIB (Master Information Block), SIB(System Information Block))), other signals, or combinations thereof.Further, an RRC message may be referred to as RRC signaling. Further, anRRC message may be, for example, an RRC connection setup message, an RRCconnection reconfiguration message, or the like.

An aspect/embodiment described in the present specification may beapplied to a system that uses LTE (Long Term Evolution), LTE-A(LIE-Advanced), SUPER 3G, IMI-Advanced, 4G, 5G, FRA (Future RadioAccess), W-CDMA (registered trademark), GSM (registered trademark),CDMA2000, UMB (Ultra Mobile Broadband), IEEE 802.11 (Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, UWB (Ultra-WideBand), Bluetooth (registeredtrademark), other appropriate systems, and/or a next generation systemenhanced based thereon.

Determination or judgment may be performed according to a value (0 or 1)represented by a bit, may be performed according to a boolean value(true or false), or may be performed according to comparison ofnumerical values (e.g., comparison with a predetermined value).

It should be noted that the terms described in the present specificationand/or terms necessary for understanding the present specification maybe replaced by terms that have the same or similar meaning. For example,a channel and/or a symbol may be a signal. Further, a signal may be amessage.

There is a case in which a UE may be referred to as a subscriberstation, a mobile unit, subscriber unit, a wireless unit, a remote unit,a mobile device, a wireless device, a wireless communication device, aremote device, a mobile subscriber station, an access terminal, a mobileterminal, a wireless terminal, a remote terminal, a handset, a useragent, a mobile client, a client, or some other appropriate terms.

An aspect/embodiment described in the present specification may be usedindependently, may be used in combination, or may be used by switchingaccording to operations. Further, transmission of predeterminedinformation (e.g., transmission of “it is X”) is not limited toexplicitly-performed transmission. The transmission of predeterminedinformation may be performed implicitly (e.g., explicit transmission ofpredetermined information is not performed).

As used herein, the term “determining” may encompasses a wide variety ofactions. For example, “determining” may be regarded as calculating,computing, processing, deriving, investigating, looking up (e.g.,looking up in a table, a database or another data structure),ascertaining and the like. Also, “determining” may be regarded asreceiving (e.g., receiving information), transmitting (e.g.,transmitting information), inputting, outputting, accessing (e.g.,accessing data in a memory) and the like. Also, “determining” may beregarded as resolving, selecting, choosing, establishing, comparing andthe like. That is, “determining” may be regarded as a certain type ofaction related to determining.

As used herein, the phrase “based on” does not mean, unless otherwisenoted, “based on only”. In other words, the phrase “base on” means both“based on only” and “based on at least”.

Also, the order of processing steps, sequences or the like of anaspect/embodiment described in the present specification may be changedas long as there is no contradiction. For example, in a method describedin the present specification, elements of various steps are presented inan exemplary order. The order is not limited to the presented specificorder.

Input/output information, etc., may be stored in a specific place (e.g.,memory) or may be stored in a management table. The input/outputinformation, etc., may be overwritten, updated, or added. Outputinformation, etc., may be deleted. Input information, etc., may betransmitted to another apparatus.

Transmission of predetermined information (e.g., transmission of “it isX”) is not limited to explicitly-performed transmission. Thetransmission of predetermined information may be performed implicitly(e.g., explicit transmission of predetermined information is notperformed).

Information, a signal, etc., described in the present specification maybe represented by using any one of the various different techniques. Forexample, data, an instruction, a command, information, a signal, a bit,a symbol, a chip or the like described throughout in the presentspecification may be represented by voltage, current, electromagneticwaves, magnetic fields or a magnetic particle, optical fields or aphoton, or any combination thereof.

The present invention is not limited to the above embodiments andvarious variations, modifications, alternatives, replacements, etc., maybe included in the present invention without departing from the spiritof the invention.

The present application is based on and claims priority to Japanesepatent application No. 2016-079185 filed on Apr. 11, 2016, and Japanesepatent application No. 2016-192350 filed on Sep. 29, 2016, the entirecontents of which are hereby incorporated by reference.

EXPLANATIONS OF LETTERS OR NUMERALS

-   UE user equipment-   eNB base station-   101 signal transmission unit-   102 signal receiving unit-   103 detection unit-   104 selection unit-   201 signal transmission unit-   202 signal receiving unit-   203 notification unit-   301 RF module-   302 BB processing module-   303 UE control module-   304 communication IF-   401 RF module-   402 BB processing module-   403 device control module

1. User equipment that selects a resource for transmitting a signalbased on a sensing result, the user equipment comprising: a detectionunit that detects, by performing sensing in a time window for sensing,one or more resources capable of transmitting a signal in a time windowfor resource selection after the time window for sensing; a selectionunit that selects a resource for transmitting a signal from the one ormore detected resources; and a transmission unit that transmits thesignal using the selected resource for transmitting the signal.
 2. Theuser equipment according to claim 1, wherein the time window forresource selection is shorter than the time window for sensing.
 3. Theuser equipment according to claim 1, wherein, upon detecting a pluralityof resources by the detection unit, the selection unit determinesautonomously or based on an instruction from a base station whether torandomly select a resource for transmitting the signal from theplurality of resources or to select a resource for transmitting thesignal based on predetermined conditions.
 4. The user equipmentaccording to claim 1, wherein start timing and end timing of the timewindow for sensing and start timing and end timing of the time windowfor resource selection are dynamically determined based on a timing atwhich the selection unit selects a resource for transmitting a signal,or correspond to timings of a boundary of a periodic period set inadvance.
 5. The user equipment according to claim 1, wherein thedetection unit detects one or more resources capable of reservingtransmission of a signal in a time window for resource reservation afterthe time window for sensing by performing sensing in the time window forsensing, the selection unit selects a resource for reservingtransmission of a signal from the one or more detected resources capableof reserving transmission of a signal, and the transmission unittransmits reservation information, which indicates that a signal isscheduled to be transmitted with a resource for reserving transmissionof the signal, using a resource for transmitting the signal.
 6. The userequipment according to claim 1, wherein the detection unit virtuallymeasures a reception quality of periodic resources by performing sensingin the time window for sensing for periodic resources after the selectedresource for transmitting the signal, and detects one or more resourcescapable of transmitting a signal in the time window for resourceselection based on the measured virtual reception quality.
 7. A signaltransmission method to be executed by user equipment that selects aresource for transmitting a signal based on a sensing result,comprising: a step of detecting, by performing sensing in a time windowfor sensing, one or more resources capable of transmitting a signal in atime window for resource selection after the time window for sensing; astep of selecting a resource for transmitting a signal from the one ormore detected resources; and a step of transmitting the signal using theselected resource for transmitting the signal.
 8. The user equipmentaccording to claim 2, wherein, upon detecting a plurality of resourcesby the detection unit, the selection unit determines autonomously orbased on an instruction from a base station whether to randomly select aresource for transmitting the signal from the plurality of resources orto select a resource for transmitting the signal based on predeterminedconditions.
 9. The user equipment according to claim 2, wherein starttiming and end timing of the time window for sensing and start timingand end timing of the time window for resource selection are dynamicallydetermined based on a timing at which the selection unit selects aresource for transmitting a signal, or correspond to timings of aboundary of a periodic period set in advance.
 10. The user equipmentaccording to claim 3, wherein start timing and end timing of the timewindow for sensing and start timing and end timing of the time windowfor resource selection are dynamically determined based on a timing atwhich the selection unit selects a resource for transmitting a signal,or correspond to timings of a boundary of a periodic period set inadvance.
 11. The user equipment according to claim 2, wherein thedetection unit detects one or more resources capable of reservingtransmission of a signal in a time window for resource reservation afterthe time window for sensing by performing sensing in the time window forsensing, the selection unit selects a resource for reservingtransmission of a signal from the one or more detected resources capableof reserving transmission of a signal, and the transmission unittransmits reservation information, which indicates that a signal isscheduled to be transmitted with a resource for reserving transmissionof the signal, using a resource for transmitting the signal.
 12. Theuser equipment according to claim 3, wherein the detection unit detectsone or more resources capable of reserving transmission of a signal in atime window for resource reservation after the time window for sensingby performing sensing in the time window for sensing, the selection unitselects a resource for reserving transmission of a signal from the oneor more detected resources capable of reserving transmission of asignal, and the transmission unit transmits reservation information,which indicates that a signal is scheduled to be transmitted with aresource for reserving transmission of the signal, using a resource fortransmitting the signal.
 13. The user equipment according to claim 4,wherein the detection unit detects one or more resources capable ofreserving transmission of a signal in a time window for resourcereservation after the time window for sensing by performing sensing inthe time window for sensing, the selection unit selects a resource forreserving transmission of a signal from the one or more detectedresources capable of reserving transmission of a signal, and thetransmission unit transmits reservation information, which indicatesthat a signal is scheduled to be transmitted with a resource forreserving transmission of the signal, using a resource for transmittingthe signal.
 14. The user equipment according to claim 2, wherein thedetection unit virtually measures a reception quality of periodicresources by performing sensing in the time window for sensing forperiodic resources after the selected resource for transmitting thesignal, and detects one or more resources capable of transmitting asignal in the time window for resource selection based on the measuredvirtual reception quality.
 15. The user equipment according to claim 3,wherein the detection unit virtually measures a reception quality ofperiodic resources by performing sensing in the time window for sensingfor periodic resources after the selected resource for transmitting thesignal, and detects one or more resources capable of transmitting asignal in the time window for resource selection based on the measuredvirtual reception quality.
 16. The user equipment according to claim 4,wherein the detection unit virtually measures a reception quality ofperiodic resources by performing sensing in the time window for sensingfor periodic resources after the selected resource for transmitting thesignal, and detects one or more resources capable of transmitting asignal in the time window for resource selection based on the measuredvirtual reception quality.
 17. The user equipment according to claim 5,wherein the detection unit virtually measures a reception quality ofperiodic resources by performing sensing in the time window for sensingfor periodic resources after the selected resource for transmitting thesignal, and detects one or more resources capable of transmitting asignal in the time window for resource selection based on the measuredvirtual reception quality.